The invention relates to a seal for a chamber doctor blade of a printing machine.
Printing machines, such as flexographic printing machines, have an applicator roller, which applies the printing ink on the actual impression cylinder and which is inked, in turn, with the help of a chamber doctor blade. The chamber doctor blade has a housing, which extends over the whole length of the applicator roller and carries at least two doctor blades, which wipe off the periphery of the rotating applicator roller and, together with the housing of the chamber doctor blade and the peripheral surface of the applicator roller lying between the doctor blades, form the boundary of an inking chamber. At its surface, the applicator roller has at least a regular screen of flat cells, which are filled with the printing ink, when the peripheral section in question of the applicator roller moves through the inking chamber, and which then deliver the printing ink, so taken up, to the impression cylinder.
The seals, which form the object of the following invention, close off the inking chamber at the ends.
Conventional seals of this type have a block of a pliable material, for example, of felt, which is inserted between the two doctor blades into the housing of the chamber doctor blade and lies closely against the two doctor blades, as well as against the section of the surface of the applicator roller lying between the doctor blades. The pliability of the sealing block makes a good seal possible at the periphery of the applicator roller and permits the chamber doctor blades to be placed increasingly strongly against the applicator roller to correspond to the advancing wear of the doctor blade.
In the case of conventional seals, the material of the sealing block must satisfy different requirements, which in the past could not always be reconciled with one another. On the one hand, it must be ensured that the inking chamber is sealed reliably and permanently. On the other hand, however, in view of the frictional contact between the sealing block and the rotating applicator roller, the seal should have the highest possible abrasion resistance, so that the sealing block is not worn down too rapidly. Moreover, the material must be chemically and mechanically resistant to the printing inks and solvents used. The liquids, which may come into contact with the surface of the sealing block, can lead, on the one hand, to swelling and softening of the material and, on the other, after the liquid has dried out, an embrittlement of the material. In the final analysis, there is increased wear of the sealing blocks in both cases.